1. Field of the Invention
The invention relates to fault detection in paper sheet or web processing systems and more particularly to detection of faulty window construction in such systems.
2. Description of the Prior Art
In envelope making machines, and the like, of the type in which a continous web of patterned documents, called foldover self-mailers, is transported between a plurality of work stations, faults may arise during the die-cutting of a window opening in each pattern and during the securement of a transparent patch overlay atop the window opening. Such faults may occur in the form of hanging die-cuts where improper cutting results in paper blockage covering the window opening, or in the form of a missing window patch which leaves a naked opening in the envelope.
When these operations are performed at high speeds typical of those used in a web-offset printing press, it is very difficult to visually detect such faults in the web. Additionally, these faults are generally undesirable in any computer printing system, but where the media may include confidential information, such as pre-numbered checks, a missing window overlay is usually intolerable. Thus, it is desirable to provide a visual or audible relay of information which will signal the machine operator that a system fault has occurred.
Furthermore, where a multiple succession of such faults occur indicative of a machine jam, patch depletion, adhesive depletion or a die shoe worn to a point where it is no longer cutting properly, it is desirable to effectuate press slow-down in addition to the audible operator indication of fault occurrence. A press slow-down would prevent excessive waste of materials and guard against a more serious equipment failure. By automatically shifting the press to slow-run the operator has time to stop the press in an orderly fashion.
A desirable solution to this problem is to utilize a high speed detector for actuating controlling circuitry which operates fault occurrence indicators and which additionally may effectuate press slow down if a sequential predetermined number of consecutive faults arise.